Gonorrhea rates in the United States have fallen to their lowest level on record, but rates of two other sexually transmitted diseases, syphilis and chlamydia, are rising, federal health officials said yesterday. The rates, though of concern, are low compared with years ago. Still, an estimated 19 million new infections of sexually transmitted diseases, or S.T.D.'s, occurred in 2004 at estimated health care costs of $19 billion, officials from the Centers for Disease Control and Prevention said. Many cases of the three bacterial diseases reported yesterday go undetected, while many diagnosed cases are not reported. Also, two common viral diseases,...